Impact of Water Vapor and Oxygen Atmosphere on Carrier Dynamics of CH ₃ NH ₃ PbI ₃ Perovskites

Organic-inorganic hybrid perovskites have garnered significant attention in the field of photovoltaics due to their exceptional optoelectronic properties. However, their sensitivity to environmental factors, such as water vapor and oxygen, remains a significant challenge to long-term stability, and the mechanisms underlying their interaction with perovskites are still not yet fully understood. This study investigates how water vapor and oxygen influence carrier dynamics in CH₃NH₃PbI₃ perovskite films by employing a combination of high-sensitivity transient absorption spectroscopy (TAS) and time-resolved photoluminescence (TRPL). The results demonstrate that both water vapor and oxygen effectively passivate deep traps, while exhibiting inertness toward shallow traps, thus prolonging carrier lifetimes. Notably, the passivation effect induced by oxygen is nearly fully reversible, in contrast to the partially reversible effect of water vapor. Furthermore, carrier lifetimes increase monotonically with rising water vapor pressure, whereas oxygen passivation is significantly more efficient: as low as 100 ppm or even less oxygen can induce the saturation of oxygen passivation. These insights into the ambient-induced modulation of carrier recombination dynamics provide a critical foundation for developing strategies to enhance the operational stability of perovskite solar cells.